Resolving global versus local/regional Pu sources in the environment using sector ICP-MS

Sector inductively coupled plasma mass spectrometry is a versatile method for the determination of plutonium activities and isotopic compositions in samples containing this element at fallout levels. Typical detection limits for Pu239 + 240 are 0.1, 0.02 and 0.002 Bq kg(-1) Pu for samples sizes of 0.5 g, 3 g, and 50 g of soil, respectively. The application of sector ICP-MS-based Pu determinations is demonstrated in studies in sediment chronology, soil Pu inventory and depth distribution, and the provenance of global fallout versus local or regional Pu sources. A sediment core collected from Sloans Lake (Denver, Colorado, USA) exhibits very similar Cs-137 and Pu239 + 240 activity profiles; Pu-240/Pu-239 atom ratios indicate possible small influences from the Nevada Test Site and/or the Rocky Flats Environmental Technology Site. An undisturbed soil profile from Lockett Meadow (Flagstaff, Arizona, USA) exhibits an exponential decrease in Pu239 + 240 activity versus depth; Pu-240/Pu-239 in the top 3 cm is slightly lower than the global fallout range of 0.180 +/- 0.014 due to possible regional influence of Nevada Test Site fallout. The (239 +/-) Pu-240 inventory at Lockett Meadow is 56 +/- 4 Bq m(-2), consistent with Northern Hemisphere mid-latitude fallout. Archived NdF3 sources, prepared from Polish soils, demonstrate that substantial Pu239 + 240 from the 1986 Chernobyl disaster has been deposited in north eastern regions of Poland; compared to global fallout, Chernobyl Pu exhibits higher abundances of Pu-240 and Pu-241. The ratios Pu-240/Pu-239 and Pu-241/Pu-239 co-vary and range from 0.186-0.348 and 0.0029-0.0412, respectively, in forest soils (Pu-241/Pu-239 = 0.2407.[Pu-240/Pu-239] - 0.0413; r(2) = 0.9924).